Note: Descriptions are shown in the official language in which they were submitted.
CA 02762075 2011-12-16
DESCRIPTION
MOVING PICTURE CODING METHOD AND MOVING PICTURE
DECODING METHOD
Technical Field
The present invention relates to moving picture coding
methods and moving picture decoding methods, and particularly to
methods for performing inter picture prediction coding and inter
picture prediction decoding of a current picture using previously
io processed pictures as reference pictures.
Background Art
In moving picture coding, data amount is generally
compressed by utilizing the spatial and temporal redundancies that
exist within a moving picture. Generally speaking, frequency
transformation is used as a method utilizing the spatial
redundancies, and inter picture prediction coding is used as a
method utilizing the temporal redundancies.. In the inter. picture
prediction coding, for coding a current picture, previously coded
pictures earlier or later than the current picture in display order are
used as reference pictures. The amount of motion of the current
picture from the reference picture is estimated, and the difference
between the picture data obtained by motion compensation based
on that amount of motion and the picture data of the current picture
is calculated, so that the temporal redundancies are eliminated.
The spatial redundancies are further eliminated from this
differential value so as to compress the data amount of the current
picture.
In the moving picture coding method called H.264 which has
3o been developed for standardization, a picture which is coded not
using inter picture prediction but using intra picture coding is
referred to as an I-picture, a picture which is coded using inter
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picture prediction with reference to one previously processed
picture which is earlier or later than a current picture in display
order is referred to as a P-picture, and a picture which is coded using
inter picture prediction with reference to two previously processed
pictures which are earlier or later than a current picture in display
order is referred to as a B-picture (See ISO/IEC 14496-2
"Information technology - Coding of audio-visual objects - Part2:
Visual" pp.218-219).
Fig. 1A is a diagram showing relationship between respective
io pictures and the corresponding reference pictures in the
above-mentioned moving picture coding method, and Fig. 1B is a
diagram showing the sequence of the pictures in the bit stream
generated by coding.
A picture 11 is an I-picture, pictures P5, P9 and P13 are
P-pictures, and pictures B2, B3, B4, B6, B7, B8, B10, B11 and B12
are B-pictures. As shown by the arrows, the P-pictures P5, P9 and
P13 are coded using inter picture prediction from the I-picture I1
and P-pictures P5 and P9 respectively as reference pictures.
As shown by the arrows, the B-pictures B2., B3 and B4 are
coded using inter picture prediction from the I-picture I1 and
P-picture P5 respectively as reference pictures. In the same
manner, the B-pictures B6, B7 and B8 are coded using the P-pictures
P5 and P9 respectively as reference pictures, and the B-pictures B10,
B11 and B12 are coded using the P-pictures P9 and P13 respectively
as reference pictures.
In the above-mentioned coding, the reference pictures are
coded prior to the pictures which refer to the reference pictures.
Therefore, the bit stream is generated by the above coding in the
sequence as shown in Fig. 1B.
By the way, in the H.264 moving picture coding method, a
coding mode called direct mode can be selected. An inter picture
prediction method in direct mode will be explained with reference to
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Fig. 2. Fig. 2 is an illustration showing motion vectors in direct
mode, and particularly showing the case of coding a block a in the
picture B6 in direct mode. In this case, a motion vector c used for
coding a block b in the picture P9 is utilized. The block b is
co-located with the block a and the picture P9 is a backward
reference picture of the picture B6. The motion vector c is a vector
used for coding the block b and refers to the picture P5. The block
a is coded using bi-prediction based on the reference blocks
obtained from the forward reference picture P5 and the backward
io reference picture P9 using vectors parallel to the motion vector c.
In other words, the motion vectors used for coding the block a are
the motion vector d for the picture P5 and the motion vector e for the
picture P9.
However, when B-pictures are coded using inter picture
prediction with reference to I and P-pictures, the temporal distance
between the current B-picture and the reference picture may be long,
which causes reduction of coding efficiency. Particularly when a lot
of B-pictures are located between adjacent I-picture and P-picture
or two P-pictures closest to each other, coding efficiency is
significantly reduced.
The present invention has been conceived in order to solve
the above-mentioned problem, and it is an object of the present
invention to provide a moving picture coding method and a moving
picture decoding method for avoiding efficiency reduction of coding
B-pictures if a lot of B-pictures are located between an I-picture and
a P-picture or between two P-pictures. In addition, it is another
object to provide a moving picture coding method and a moving
picture decoding method for improving coding efficiency in direct
mode.
Disclosure of Invention
In order to achieve above-mentioned object, the moving
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picture coding method of the present invention is a moving picture
coding method for coding picture data corresponding to pictures
that form a moving picture and generating a bit stream, the moving
picture coding method comprising: a coding step for coding a
current picture as one of an I-picture, a P-picture and a B-picture,
the I-picture having only blocks which are intra picture coded, the
P-picture having a block which is inter picture prediction coded with
uni-predictive reference using a previously coded picture as a first
reference picture, and the B-picture having a block which is inter
io picture prediction coded with bi-predictive reference using
previously coded pictures as a first reference picture and a second
reference picture, wherein the coding step includes a control step
for determining coding order which is different from display order for
consecutive B-pictures located between I-pictures and P-pictures.
Therefore, since B-pictures can be coded using pictures which
are temporally closer in display order as reference pictures,
prediction efficiency for motion compensation is improved and thus
coding efficiency can be increased.
Also, the moving picture coding method according to the
present invention is a moving picture coding method for coding
picture data corresponding to pictures that form a moving picture
and generating a bit stream, the moving picture coding method
comprising: a coding step for coding a current picture as a B-picture
having a block which is inter picture prediction coded with
bi-predictive reference using previously coded pictures as a first
reference picture and a second reference picture, wherein in the
coding step, when a current block A in a current B-picture is coded
in direct mode by which motion compensation of the current block A
is performed using motion vectors of the current block A obtained
from a motion vector of a previously coded block, the motion vectors
for performing the motion compensation of the current block A are
obtained by scaling a first motion vector, based on a first reference
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picture, of a co-located block B in the second reference picture of the
current block A. using a difference specified by information
indicating display order of pictures.
Therefore, when the direct mode is selected, since a first
motion vector of a second reference picture is scaled, there is no
need to add motion vector information to a bit stream, and
prediction efficiency can also be improved.
Likewise, when a current block A in a current B-picture is
coded in direct mode, the motion vectors for performing the motion
io compensation of the current block A may be obtained by scaling a
second motion vector, based on a second reference picture, of a
co-located block B in the second reference picture of the current
block A, using a difference specified by information indicating
display order of pictures.
Therefore, when the direct mode. is selected, since a second
motion vector of a second reference picture is scaled, there is no
need to add motion vector information to a bit stream, and
prediction efficiency can also be improved.
Furthermore, when a current block A in a current B-picture is
coded in direct mode, if a co-located block B in the second reference
picture of the current block A is previously coded in direct mode, the
motion vectors for performing the motion compensation of the
current block A may be obtained by scaling a first motion vector,
based on a first reference picture of the block B, substantially used
for coding the block B in the second reference picture, using a
difference specified by information indicating display order of
pictures.
Therefore, when the direct mode is selected, since a first
motion vector of a second reference picture which has been
substantially used for coding the second reference picture is scaled,
there is no need to add motion vector information to a bit stream,
and prediction efficiency can also be improved.
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Also, when a current block A in a current B-picture is coded in
direct mode, the motion vectors for performing the motion
compensation of the current block A may be obtained by scaling a
first motion vector, based on a first reference picture, of a co-located
block B in a temporally later P-picture, using a difference specified
by information indicating display order of pictures.
Therefore, when the direct mode is selected, since a first
motion vector of a temporally later P-picture is scaled, there is no
need to add motion vector information to a bit stream, and
1o prediction efficiency can also be improved.
Furthremore, when a current block A in a current B-picture is
coded in direct mode, the motion vectors for performing the motion
compensation of the current block A may be obtained by scaling a
first motion vector if a co-located block B in the second reference
picture of the current block A is coded using at least the first motion
vector based on a first reference picture of the block B, and scaling
a second motion vector if the block B is coded using only the second
motion vector based on a second reference picture of the block B,
using a difference specified by information indicating display order
of pictures.
Therefore, when the direct mode is selected, if a second
reference picture has a first motion vector, this first motion vector is
scaled, and if the second reference picture does not have a first
motion vector but only a second motion vector, this second motion
vector is scaled. So, there is no need to add motion vector
information to a bit stream, and prediction efficiency can be
improved.
In addition, the moving picture decoding method according to
the present invention is a moving picture decoding method for
3o decoding a bit stream which is generated by coding picture data
corresponding to pictures that form a moving picture, the moving
picture decoding method comprising: a decoding step for decoding a
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current picture by inter picture prediction using a previously
decoded picture as a reference picture, wherein in the decoding step,
when the current picture is decoded by the inter picture prediction
with bi-predictive reference using the previously decoded pictures
as a first reference picture and a second reference picture, a bit
stream including at least a picture which is temporally closest to the
current picture in display order, as the first reference picture or the
second reference picture, is.decoded.
Therefore, a bit stream, which is generated by coding a
io picture by inter picture prediction with bi-predictive reference using
pictures which are temporally close in display order as a first
reference picture and a second reference picture, can be properly
decoded.
Also, the moving picture decoding method according to the
present invention is a moving picture decoding method for decoding
a bit stream which is generated by coding picture data
corresponding to pictures that form a moving picture, the moving
picture decoding method comprising: a decoding step for decoding a
current picture by inter picture prediction using a previously
decoded picture as a reference picture, wherein in the decoding step,
when the current picture is a picture having a block which is decoded
by inter picture prediction with bi-predictive reference using
previously decoded pictures as a first reference picture and a second
reference picture, and a current block A is decoded in direct mode by
which motion compensation of the current block A is performed
using motion vectors of the current block A obtained from a motion
vector of a previously decoded block, the motion vectors for
performing the motion compensation of the current block A are
obtained by scaling a first motion vector, based on a first reference
picture, of a co-located block B in the second reference picture of the
current block A, using a difference specified by information
indicating display order of pictures.
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Therefore, when the direct mode is selected, since a first
motion vector of a second reference picture is scaled, proper
decoding can be achieved.
Likewise, when a current picture is a picture having a block
which is decoded by inter picture prediction with bi-predictive
reference and a current block A is decoded in direct mode, the
motion vectors for performing the motion compensation of the
current block A may be obtained by scaling a second motion vector,
based on a second reference picture, of a co-located block B in the
io second reference picture of the current block A, using a difference
specified by information indicating display order of pictures.
Therefore, when the direct mode is selected, since a second
motion vector of a second reference picture is scaled, proper
decoding can be achieved.
Furthermore, when a current picture is a picture having a
block which is decoded by inter picture prediction with bi-predictive
reference and a current block A is decoded in direct mode, if a
co-located block B in the second reference picture of the current
block A is previously decoded in direct mode, the motion vectors for
performing the motion compensation of the current block A may be
obtained by scaling a first motion vector, based on a first reference
picture of the block B, substantially used for decoding the block B in
the second reference picture, using a difference specified by
information indicating display order of pictures.
Therefore, when the direct mode is selected, since a first
motion vector of a second reference picture which has been
substantially used for decoding the second reference picture is
scaled, proper decoding can be achieved.
Also, when a current picture is a picture having a block which
is decoded by inter picture prediction with bi-predictive reference
and a current block A is decoded in direct mode, the motion vectors
for performing the motion compensation of the current block A may
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be obtained by scaling a first motion vector, based on a first
reference picture, of a co-located block B in a temporally later
picture, using a difference specified by information indicating
display order of pictures, the later picture being inter picture
prediction decoded with uni-predictive reference using a previously
decoded picture as a first reference picture.
Therefore, when the direct mode is selected, since a first
motion vector of .a picture which is decoded by inter picture
prediction with uni-predictive reference is scaled, proper decoding
io can be achieved.
The present invention can be realized as such a moving
picture coding method and a moving picture decoding method as
mentioned above, but also as a moving picture coding apparatus and
a moving picture decoding apparatus including characteristic steps
of these moving picture coding method and moving picture decoding
method. In addition, the present invention can be realized as a bit
stream obtained by coding by the moving picture coding method so
as to distribute it via a recording medium such as a CD-ROM or a
transmission medium such as the Internet.
Brief Description of Drawings
Fig. 1 is a schematic diagram showing prediction relations
between pictures and their sequence in the conventional moving
picture coding method, and 1A shows the relations between
respective pictures and the corresponding reference pictures, and
Fig. 113 shows the sequence of the pictures in a bit stream generated
by coding.
Fig. 2 is a schematic diagram showing motion vectors in direct
mode in the conventional moving picture coding method.
Fig. 3 is a block diagram showing the structure of a first
embodiment of a moving picture coding apparatus using a moving
picture coding method according to the present invention.
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Figs 4A and 4B are an illustration of picture numbers and relative indices
in the embodiments of the present invention.
Fig. 5 is a conceptual illustration of a moving picture coded
data format in the moving picture coding apparatus in the
embodiments of the present invention.
Fig. 6 is an illustration, showing the picture sequence in a
reordering memory 'in the embodiments of the present invention,
and Fig. 6A shows the sequence in input order, and Fig. 6B shows the
reordered sequence.
Fig. 7 is a schematic diagram showing motion vectors in direct
mode in the embodiments of the present invention, and Fig. 7A
shows a case where a current block a is a picture B7, Fig. 7B shows
first and second examples in A. case where a current block a is a
picture B6, Fig. 7C shows a third example in a case where a current .
block a is a picture B6, and Fig. 7D shows a fourth example in a case
where a current block a is a picture B6.
Fig. 8 is a schematic diagram showing motion vectors in direct
mode in the embodiments of the present invention, and Fig. 8A
shows a fifth example in. a case where a current block a is a picture
B6, Fig. 8B shows a sixth example in a case where a current block a
is a picture B6, Fig. 8C shows a seventh example in a case where a
current block a is a picture B6, and Fig. 8D shows a case where a
current block a is a picture B8.
Fig. 9 is a schematic diagram showing prediction relations
between respective pictures and their sequence in the embodiments
of the present invention, and Fig. 9A shows the prediction relations
between respective pictures indicated in display order, and Fig. 9B
shows the sequence of the pictures reordered in coding order (in a
bit stream).
Fig..10 is a schematic diagram showing prediction relations
between respective pictures and their sequence in the embodiments
of the present invention, and Fig. 10A shows the prediction relations
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between respective pictures indicated in display order, and :Fig. 10B
shows the sequence of the pictures reordered' in coding order '(in *.a
bit stream).
Fig. 11 'is a schematic diagram showing prediction relations
between respective pictures and their sequence in the embodiments
of the present invention, and. Fig. 11A shows the prediction.;reiations
between respective pictures indicated in display order, and Fig. 11B
shows the sequence of the pictures reordered in coding order (i.n a
bit stream).
Fig. 12 is a schematic diagram showing hierarchically the
picture prediction structure as shown in Fig. 6 in the embodiments of
the present invention.
Fig. 13 is a schematic diagram showing hierarchically the
picture prediction structure as shown in Fig. 9 in the embodiments of
i5 the present invention.
Fig. 14 is a schematic diagram showing hierarchically the
picture prediction structure as shown in Fig. 10 in the embodiments,
of the present invention.
Fig. 15 is a schematic. diagram showing hierarchically the-
picture prediction structure as shown in Fig. 11 in the embodiments -
of the present invention.
Fig. 1.6 As a block diagram showing the structure of an
embodiment of a moving picture decoding apparatus using a moving
picture decoding method according to the present invention.
Fig-. 17 is an illustration of a recording medium for storing a
program for realizing the moving picture coding method and the
moving picture - decoding ' method in the first and , second
embodiments by a computer system, and Fig. 17A shows an
example of a physical format. of a flexible disk as a body of recording
medium, Fig. 17B shows a cross-sectional view and a front view of
the appearance of the flexible disk and the flexible disk itself, Fig.
17C shows a structure for recording and reproducing the program on
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the flexible disk FD.
Fig. 18 a block diagram showing the overall configuration of a
content supply system for realizing content distribution service.
Fig. 19 is a sketch showing an example of a mobile phone.
Fig. 20 is a block diagram showing the internal structure of
the mobile phone.
Fig. 21 is a block diagram showing the overall configuration of
a digital broadcast system.
1o Best Mode for Carrying Out the Invention
The embodiments of the present invention will be explained
below with reference to the figures.
(First Embodiment)
Fig. 3 is a block diagram showing the structure of an
embodiment of the moving picture coding apparatus using the
moving picture coding method according to the present invention.
As shown in Fig. 3, the moving picture coding apparatus
includes a reordering memory 101, a difference calculation unit 102,
a residual error coding unit 103, a bit stream generation unit 104, a
residual error decoding unit 105, an addition unit 106, a reference
picture memory 107, a motion vector estimation unit 108, a mode
selection unit 109, a coding control unit 110, switches 111^-115 and
a motion vector storage unit 116.
The reordering memory 101 stores moving pictures inputted
on a picture-to-picture basis in display order. The coding control
unit 110 reorders the pictures stored in the reordering memory 101
in coding order. The coding control unit 110 also controls the
operation of the motion vector storage unit 116 for storing motion
vectors.
Using the previously coded and decoded picture data as a
reference picture, the motion vector estimation unit 108 estimates a
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motion vector indicating a position which is predicted optimum in
the search area in the reference picture. The mode selection unit
109 determines a mode for coding macroblocks using the motion
vector estimated by the motion vector estimation unit 108, and
generates predictive image data based on the coding mode. The
difference calculation unit 102 calculates the difference between the
image data read out from the reordering memory 101 and the
predictive image data inputted by the mode selection unit 109, and
generates residual error image data.
The residual error coding unit 103 performs coding processing
such as frequency transform and quantization on the inputted
residual error image data for generating the coded data. The bit
stream generation unit 104 performs variable length coding or the
like on the inputted coded data, and further adds the motion vector
information, the coding mode information and other relevant
information inputted by the mode selection unit 109 to the coded
data so as to generate a bit stream.
The residual error decoding unit 105 performs decoding
processing such as inverse quantization and inverse frequency
transform on the inputted coded data for generating decoded
differential image data. The addition unit 106 adds the decoded
differential image data inputted by the residual error decoding unit
105 and the predictive image data inputted by the mode selection
unit 109 for generating decoded image data. The reference picture
memory 107 stores the generated decoded image data.
Fig. 4 is an illustration of pictures and relative indices. The
relative indices are used for identifying uniquely reference pictures
stored in the reference picture memory 107, and they are associated
to respective pictures as shown in Fig. 4. The relative indices are
3o also used for indicating the reference pictures which are to be used
for coding blocks using inter picture prediction.
Fig. 5 is a conceptual illustration of moving picture coded data
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format used by the moving picture coding apparatus. Coded data
"Picture" for one picture includes header coded data "Header"
included in the head of the picture, block coded data "Blocks" for
direct mode, block coded data "Block2" for the inter picture
prediction other than the direct mode, and the like. The block
coded data "Block2" for the inter picture prediction other than direct
mode has a first relative index "RIdxl" and a second relative index
"RIdx2" for indicating two reference pictures used for inter picture
prediction, a first motion vector "MV1" and a second motion vector
to "MV2" in this order. On the other hand, the block coded data
"Blocks" for direct mode does not have the first and second relative
indices "RIdxl" and "RIdx2" and the first and second motion vectors
"MV1" and "MV2". The index which is to be used, the first relative
index "RIdx1" or the second relative index "RIdx2", can be
determined by the prediction type "PredType". Also, the first
relative index "RIdxl" indicates a first reference picture, and the
second relative index "RIdx2" indicates a second reference picture.
In other words, whether a picture is a first reference picture or a
second reference picture is determined based on where they are
located in the bit stream.
Note that a P-picture is coded by inter picture prediction with
uni-predictive reference using a previously coded picture which is
located earlier or later in display order as a first reference picture,
and a B-picture is coded by inter picture prediction with bi-predictive
reference using previously coded pictures which are located earlier
or later in display order as a first reference picture and a second
reference picture. In the first embodiment, the first reference
picture is explained as a forward reference picture, and the second
reference picture is explained as a backward reference picture.
3o Furthermore, the first and second motion vectors for the first and
second reference pictures are explained as a forward motion vector
and a backward motion vector respectively.
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Next, how to assign the first and second relative indices will
be explained with reference to Fig. 4A.
As the first relative indices, in the information indicating
display order, the values incremented by 1 from 0 are first assigned
to the reference pictures earlier than the current picture from the
picture closer to the current picture. After the values incremented
by 1 from 0 are assigned to all the reference pictures earlier than the
current picture, then the subsequent values are assigned to the
reference pictures later than the current picture from the picture
1o closer to the current picture.
As the second relative indices, in the information indicating
display order, the values incremented by 1 from 0 are assigned to
the reference pictures later than the current picture from the picture
closer to the current picture. After the values incremented by 1
from 0 are assigned to all the reference pictures later than the
current picture, then the subsequent values are assigned to the
reference pictures earlier than the current picture from the picture
closer to the current picture.
For example, in Fig. 4A, when the first relative index "RIdxl"
is 0 and the second relative index "RIdx2" is 1, the forward reference
picture is the. B-picture No. 6 and the backward reference picture is
the P-picture No. 9. Here, these picture numbers 6 and 9 indicate
the display order.
Relative indices in a block are represented by variable length
code words, and the codes with shorter lengths are assigned to the
indices of the smaller values. Since the picture which is closest to
the current picture is usually selected as a reference picture for inter
picture prediction, coding efficiency is improved by assigning the
relative index values in order of closeness to the current picture.
Assignment of reference pictures to relative indices can be
changed arbitrarily if it is explicitly indicated using buffer control
signal in coded data (RPSL in Header as shown in Fig. 5). This
CA 02762075 2011-12-16
enables to change the reference picture with the second relative
index "0" to an arbitrary reference picture in the reference picture
memory 107. As shown in Fig. 4B, assignment of reference indices
to pictures can be changed, for example.
Next, the operation of the moving picture coding apparatus
structured as above will be explained below.
Fig. 6 is an illustration showing the picture sequence in the
reordering memory 101, and Fig. 6A shows the sequence in input
order and Fig. 6B shows the reordered sequence. Here, vertical
lines show pictures, and the numbers indicated at the lower right of
the pictures show the picture types (I, P and B) with the first
alphabetical letters and the picture numbers indicating display order
with the following numbers.
As shown in Fig. 6A, a moving picture is inputted to the
reordering memory 101 on a picture-to-picture basis in display order,
for example. When the pictures are inputted to the reordering
memory 101, the coding control unit 110 reorders the pictures
inputted to the reordering memory 101 in coding order. The
pictures are reordered based on the reference relations in inter
picture prediction coding, and more specifically, the pictures are
reordered so that the pictures used as reference pictures are coded
earlier than the pictures which use the reference pictures.
Here, it is assumed that a P-picture refers to one neighboring
previously processed I or P-picture which is located earlier or later
than the current P-picture in display order, and a B-picture refers to
two neighboring previously processed pictures which are located
earlier or later than the current B-picture in display order.
The pictures are coded in the following order. First, a
B-picture at the center of B-pictures (3 B-pictures in Fig. 6A, for
instance) located between two P-pictures is coded, and then another
B-picture closer to the earlier P-picture is coded. For example, the
pictures B6, B7, B8 and P9 are coded in the order of P9, B7, B6 and
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B8.
In this case, in Fig. 6A, the picture pointed by the arrow refers
to the picture at the origin of the arrow. Specifically, B-picture B7
refers to P-pictures P5 and P9, B6 refers to P5 and B7, and B8 refers
to B7 and P9, respectively. The coding control unit 110 reorders
the pictures in coding order, as shown in Fig. 6B.
Next, the pictures reordered in the reordering memory 101
are read out in a unit for every motion compensation. Here, the
unit of motion compensation is referred to as a macroblock which is
1o 16 (horizontal) x 16 (vertical) pixels in size. Coding of the pictures
P9, B7 B6 and B8 shown in Fig. 6A will be explained below in this
order.
(Coding of Picture P9)
The P-picture P9 is coded using inter picture prediction with
reference to one previously processed picture located earlier or later,
than P9 in display order. In coding P9, the picture P5 is the
reference picture, as mentioned above. P5 has already been coded
and the decoded picture thereof is stored in the reference picture
memory 107. In coding P-pictures, the coding control unit 110
controls switches 113, 114 and 115 so as to be ON. The
macroblocks in the picture P9 read out from the reordering memory
101 are thus inputted to the motion vector estimation unit 108, the
mode selection unit 109 and the difference calculation unit 102 in
this order.
The motion vector estimation unit 108 estimates a motion
vector of a macroblock in the picture P9, using the decoded picture
data of the picture PS stored in the reference picture memory 107 as
a reference picture, and outputs the estimated motion vector to the
mode selection unit 109.
The mode selection unit 109 determines the mode for coding
the macroblock in the picture P9 using the motion vector estimated
by the motion vector estimation unit 108. Here, the coding mode
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indicates the method of coding macroblocks. As for P-pictures, it
determines any of the coding methods, intra picture coding, inter
picture prediction coding using a motion vector and inter picture
prediction coding without using a motion vector (where motion is
handled as "0"). For determining a coding mode, a method is
selected so that a coding error is reduced with a small amount of
bits.
The mode selection unit 109 outputs the determined coding
mode to the bit stream generation unit 104. If the coding mode
io determined by the mode selection unit 109 is inter picture prediction
coding, the motion vector which is to be used for the inter picture
prediction coding is outputted to the bit stream generation unit 104
and further stored in the motion vector storage unit 116.
The mode selection unit 109 generates predictive image data
based on the determined coding mode for generating to the
difference calculation unit 102 and the addition unit 106. However,
when selecting intra picture coding, the mode selection unit 109
does not output predictive image data. In addition, when selecting
intra picture coding, the mode selection unit 109 controls the
switches 111 and 112 to connect to "a" side and "c" side respectively,
and when selecting inter picture prediction coding, it controls them
to connect to "b" side and "d" side respectively. The case will be .
explained below where the mode selection unit 109 selects inter
picture prediction coding.
The difference calculation unit 102 receives the image data of
the macroblock in the picture P9 read out from the reordering
memory 101 and the predictive image data outputted from the mode
selection unit 109. The difference calculation unit 102 calculates
the difference between the image data of the macroblock in the
picture P9 and the predictive image data, and generates the residual
error image data for outputting to the residual error coding unit 103.
The residual error coding unit 103 performs coding processing
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CA 02762075 2011-12-16
such as frequency transform and quantization on the inputted
residual error image data and thus generates the coded data for
outputting to the bit stream generation unit 104 and the residual
error decoding unit 105. Here, the coding processing such as
frequency transform and quantization is performed in every 8
(horizontal) x 8 (vertical) pixels or 4 (horizontal) x 4 (vertical) pixels,
for example.
The bit stream generation unit 104 performs variable length
coding or the like on the inputted coded data, and further adds
to information such as motion vectors and a coding mode, header
information and so on to the coded data for generating and
outputting the bit stream.
On the other hand, the residual error decoding unit 105
performs decoding processing such as inverse quantization and
inverse frequency transform on the inputted coded data and
generates the decoded differential image data for outputting to the
addition unit 106. The addition unit 106 adds the decoded
differential image data and the predictive image data inputted by
the mode selection unit 109 for generating the decoded image data,
and stores it in the reference picture memory 107.
That is the completion of coding one macroblock in the picture
P9. According to the same processing, the remaining macroblocks
of the picture P9 are coded. And after all the macroblocks of the
picture P9 are coded, the picture B7 is coded.
(Coding of Picture B7)
The picture B7 refers to the picture P5 as a forward reference
picture and the picture P9 as a backward reference picture. Since
the picture B7 is used as a reference picture for coding other
pictures, the coding control unit 110 controls the switches 113, 114
3o and 115 so as to be ON, which causes the macroblocks in the picture
B7 read out from the reordering memory 101 to be inputted to the
motion vector estimation unit 108, the mode selection unit 109 and
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CA 02762075 2011-12-16
the difference calculation unit 102.
Using the decoded picture data of the picture P5 and the
decoded picture data of the picture P9 which are stored in the
reference picture memory 107 as a forward reference picture and a
backward reference picture respectively, the motion vector
estimation unit 108 estimates a forward motion vector and a
backward motion vector of the macroblock in the picture B7. And
the motion vector estimation unit 108 outputs the estimated motion
vectors to the mode selection unit 109.
to The mode selection unit 109 determines the coding mode for
the macroblock in the picture B7 using the motion vectors estimated
by the motion vector estimation unit 108. Here, it is assumed that
a coding mode for B-pictures can be selected from among intra
picture coding, inter picture prediction coding using a forward
motion vector, inter picture prediction coding using a backward
motion vector, inter picture prediction coding using bi-predictive
motion vectors and direct mode.
Operation of direct mode coding will be explained with
reference to Fig. 7A. Fig. 7A is an illustration showing motion
vectors in direct mode, and specifically shows the case where the
block a in the picture B7 is coded in direct mode. In this case, a
motion vector c, which has been used for coding the block b in the
picture P9, is utilized. The block b is co-located with the block a,
and the picture P9 is a backward reference picture of the picture B7.
The motion vector 'c is stored in the motion vector storage unit 116.
The block a is bi-predicted from the forward reference picture P5 and
the backward reference picture 09 using vectors obtained utilizing
the motion vector c. For example, as a method of utilizing the
motion vector c, there is a method of generating motion vectors
parallel to the motion vector c. In this case, the motion vector d
and the motion vector e are used for the picture P5 and the picture
P9 respectively for coding the block a.
CA 02762075 2011-12-16
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
temporal distance between the backward reference picture P9 for
the current picture B7 and the picture P5 which the block in the
backward reference picture P9 refers to is TRD, and the temporal
distance between the current picture B7 and the forward reference
picture P5 is TRF respectively, the motion vector d MVF and the
motion vector e MVB are respectively calculated by Equation 1 and
Equation 2. Note that the temporal distance between the pictures
1o can be determined based on the information indicating the display
order (position) given to the respective pictures or the difference
specified by the information.
MVF = MV x TRF / TRD ...... Equation 1
MVB = (TRF - TRD) x MV / TRD ...... Equation 2
where MVF and MVB respectively represent horizontal components
and vertical components of the motion vectors, and the plus and
minus signs indicate directions of the motion vectors.
By the way, as for selection of a coding mode, a method for
reducing coding error with a smaller amount of bits is generally
selected. The mode selection unit 109 outputs the determined
coding mode to the bit stream generation unit 104. If the coding
mode determined by the mode selection unit 109 is inter picture
prediction coding, the motion vectors used for the inter picture
prediction coding is outputted to the bit stream generation unit 104
and further stored in the motion vector storage unit 116. When the
direct mode is selected, the motion vectors which are calculated
according to Equation 1 and Equation 2 and used for direct mode are
stored in the motion vector storage unit 116.
The mode selection unit 109 also generates predictive image
3o data based on the determined coding mode for outputting to the
difference calculation unit 102 and the addition unit 106, although it
does not output the predictive image data if it selects the intra
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CA 02762075 2011-12-16
picture coding. In addition, when selecting the intra picture coding,
the mode selection unit 109 controls the switches 111 and 112 to
connect to "a" side and "c" side respectively, and when selecting the
inter picture prediction coding or direct mode, it controls the
switches 111 and 112 to connect to "b" side and "d" side respectively.
The case will be explained below where the mode selection. unit 109
selects the inter picture prediction coding or the direct mode.
The difference calculation unit 102 receives the image data of
the macroblock of the picture B7 read out from the reordering
io memory 101 and the predictive image data outputted from the mode
selection unit 109. The difference calculation unit 102 calculates
the difference between the image data of the macroblock of the
picture B7 and the predictive image data, and generates the residual
error image data for outputting to the residual error coding unit 103.
The residual error coding unit 103 performs coding processing
such as frequency transform and quantization on the inputted
residual error image data and thus generates the coded data for
outputting to the bit stream generation unit 104 and the residual
error decoding unit 105.
The bit stream generation unit 104 performs variable length
coding or the like on the inputted coded data, and further adds
information such as motion vectors and a coding mode and so on to
that data for generating and outputting a bit stream.
On the other hand, the residual error decoding unit 105
performs decoding processing such as inverse quantization and
inverse frequency transform on the inputted coded data and
generates the decoded differential image data for outputting to the
addition unit 106. The addition unit 106 adds the decoded
differential image data and the predictive image data inputted by
the mode selection unit 109 for generating the decoded image data,
and stores it in the reference picture memory 107.
That is the completion of coding one macroblock in the picture
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CA 02762075 2011-12-16
B7. According to the same processing, the remaining macroblocks
in the picture B7 are coded. And after all the macroblocks of the
picture B7 are coded, the picture B6 is coded.
(Coding of Picture B6)
Since the picture B6 is a B-picture, B6 is coded using inter
picture prediction with reference to two previously processed
pictures located earlier or later than B6 in display order. The
B-picture B6 refers to the picture P5 as a forward reference picture
and the picture B7 as a backward reference picture, as described
io above. Since the picture B6 is not used as a reference picture for
coding other pictures, the coding control unit 110 controls the
switch 113 to be ON and the switches 114 and 115 to be OFF, which
causes the macroblock of the picture B6 read out from the
reordering memory 101 to be inputted to the motion vector
estimation unit 108, the mode selection unit 109 and the difference
calculation unit 102.
Using the decoded picture data of the picture P5 and the
decoded picture data of the picture B7 which are stored in the
reference picture memory 107 as a forward reference picture and a
backward reference picture respectively, the motion vector
estimation unit 108 estimates the forward motion vector and the
backward motion vector for the macroblock in the picture B6. And
the motion vector estimation unit 108 outputs the estimated motion
vectors to the mode selection unit 109.
The mode selection unit 109 determines the coding mode for
the macroblock in the picture B6 using the motion vectors estimated
by the motion vector estimation unit 108.
Here, the first example of direct mode coding operation for
the macroblock in the picture B6 will be explained with reference to
3o Fig. 7B. Fig. 7B is an illustration showing motion vectors in direct
mode, and specifically showing the case where the block a in the
picture B6 is coded in direct mode. In this case, a motion vector c,
23
CA 02762075 2011-12-16
which has been used for coding a block b in the picture B7, is utilized.
The block b is co-located with the block a, and the picture B7 is a
backward reference picture of the picture B6. Here, it is assumed
that the block b is coded by forward reference.only or bi-predictive
reference and the forward motion vector of the block b is the motion
vector c. It is also assumed that the motion vector c is stored in the
motion vector storage unit 116. The block a is bi-predicted from
the forward reference picture P5 and the backward reference picture
B7 using motion vectors generated utilizing the motion vector c.
1o For example, if a method of generating motion vectors parallel to the
motion vector c is used, as is the case of the above-mentioned
picture B7, the motion vector d and the motion vector e are used for
the picture P5 and the picture B7 respectively for coding the block a.
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
temporal distance between the backward reference picture B7 for
the current picture B6 and the picture P5 which the block b in the
backward reference picture B7 refers to is TRD, and the temporal
distance between the current picture B6 and the forward reference
picture PS is TRF respectively, the motion vector d MVF and the
motion vector e MVB are respectively calculated by
above-mentioned Equation 1 and Equation 2. Note that the
temporal distance between the pictures can be determined based on
the information indicating display order of the pictures or the
difference specified by the information, for instance.
As described above, in direct mode, by scaling the forward
motion vector of a backward reference B-picture, there is no need to
transmit motion vector information, and motion prediction efficiency
can be improved. Accordingly, coding efficiency can be improved.
In addition, by using reference pictures temporally closest available
in display order as a forward reference picture and a backward
reference picture, coding efficiency can be increased.
24
CA 02762075 2011-12-16
Next, the second example of the direct mode will be explained
with reference to Fig. 7B. In this case, the motion vector, which has
been used for coding the block b in the picture B7, is utilized. The
block b is co-located with the block a, and the picture B7 is a
backward reference picture for the picture B6. Here, it is assumed
that the block b has been coded in direct mode and the forward
motion vector which has been substantially used for coding the block
b is the motion vector c. Specifically, the motion vector c is
obtained by scaling the motion vector used for coding a block i,
1o co-located with the block b, in the picture P9 that is the backward
reference picture for the picture B7. The motion vector c stored in
the motion vector storage unit 116 is used, or the motion vector c is
obtained by reading out from the motion vector storage unit 116 the
motion vector of the block i in the picture P9 which has been used for
coding the block b in direct mode and calculating based on that
motion ,vector. When the motion vector which is obtained by
scaling for coding the block b in the picture B7 in direct mode is
stored in the motion vector storage unit 116, only the forward
motion vector needs to be stored. The block a is bi-predicted from
the forward reference picture P5 and the backward reference picture
B7 using the motion vectors generated utilizing the motion vector c..
For example, if a method of generating motion vectors parallel to the
motion vector c is used, as is the case of the above-mentioned first
example, motion vectors used for coding the block a are the motion
vector d and the motion vector e for the picture P5 and the picture
B7 respectively.
In this case, the forward motion vector d MVF and the
backward motion vector e MVB of the block a are respectively
calculated by above-mentioned Equation 1 and Equation 2, as in the
case of the first example.
As described above, in direct mode,. since the forward motion
vector of a backward reference B-picture which has been
CA 02762075 2011-12-16
substantially used for coding the B-picture in direct mode is scaled,
there is no need to transmit the motion vector information, and
motion prediction efficiency can be improved even if the co-located
block in the backward reference picture has been coded in direct
mode. Accordingly, coding efficiency can be improved. In
addition, by using reference pictures which are temporally closest
available in display order as a forward reference picture and a
backward reference picture, coding efficiency can be increased.
Next, the third example of direct mode will be explained with
1o reference to Fig. 7C. Fig. 7C is an illustration showing motion
vectors in direct mode, and specifically showing the case where the
block a in the picture B6 is coded in direct mode. In this case, the
motion vector which has been used for coding the block b in the
picture B7 is utilized. The picture B7 is a backward reference
picture for the picture B6, and the block b in the picture B7 is
co-located with the block a in the picture B6. Here, it is assumed
that the block b has been coded using a backward motion vector only
and the backward motion vector used for coding the block b is a
motion vector f. Specifically, the motion vector f is assumed to be
stored in the motion vector storage unit 116. The block a is
bi-predicted from the forward reference picture P5 and the backward
reference picture B7 using motion vectors generated utilizing the
motion vector f.. For example, if a method of generating motion
vectors parallel to the motion vector f is used, as is the case of the
above-mentioned first example, motion vectors used for coding the
block a are the motion vector g and the motion vector h for the
picture P5 and the picture B7 respectively.
In this case, where the forward motion vector g is MVF, the
backward motion vector h is MVB, the motion vector f is MV, the
temporal distance between the backward reference picture B7 for
the current picture B6 and the picture P9 which the block in the
backward reference picture B7 is TRD, the temporal distance
26
CA 02762075 2011-12-16
between the current picture B6 and the forward reference picture P5
is TRF, and the temporal distance between the current picture B6
and the backward reference picture B7 is TRB respectively, the
motion vector g MVF and the motion vector h MVB are respectively
calculated by Equation 3 and Equation 4.
MVF = - TRF x MV / TRD ...... Equation 3
MVB = TRB x MV / TRD ...... Equation 4
As described above, in direct mode, since the backward
motion vector of a co-located block in a backward reference
to B-picture which has been used for coding the block is scaled, there
is no need to transmit motion vector information, and motion
prediction efficiency can be improved even if the co-located block in
the backward reference picture has only the backward motion vector.
Accordingly, the coding efficiency can be improved. In addition, by
1.5 using reference pictures which are temporally closest available in
display order as a forward reference picture and a backward
reference picture, coding efficiency can be increased.
Next, the fourth example of direct mode will be explained with
reference to Fig. 7D. Fig. 7D is an illustration showing motion
20 vectors in direct mode, and specifically showing the case where the
block a in the picture B6 is coded in direct mode. In this case, the
motion vector which has been used for coding the block b in the
picture B7 is utilized. The picture B7 is the backward reference
picture for the picture B6, and the block b is co-located with the
25 block a in the picture B6. Here., it is assumed that the block b has
been coded using the backward motion vector only, as is the case of
the third example, and the backward motion vector used for coding
the block b is the motion vector f. Specifically, the motion vector f
is assumed to be stored in the motion vector storage unit 116. The
3o block a is bi-predicted from the reference picture P9 which is
referred to by the motion vector f and the backward reference
picture B7 using motion vectors generated utilizing the motion
27
CA 02762075 2011-12-16
vector f. For example if a method of generating motion vectors
parallel to the motion vector f is used, as is the case of the
above-mentioned first example, motion vectors used for coding the
block a are the motion vector g and the motion vector h for the
picture P9 and the picture B7 respectively.
In this case, where the forward motion vector g is.. MVF, the
backward motion vector h is MVB, the motion vector f is MV, the
temporal distance between the backward reference picture B7 for
the current picture B6 and the picture P9 which the block in the
io backward reference picture B7 refers to is TRD, and the temporal
distance between the current picture B6 and the picture P9 which
the block b in the backward reference picture B7 refers to is TRF
respectively, the motion vector g MVF and the motion vector h MVB
are respectively calculated by Equation 1 and Equation 2.
As described above, in direct mode, by scaling the backward
motion vector of a co-located block in a backward reference
B-picture which has been used for coding the block, there is no need
to transmit motion vector information, and motion prediction
efficiency can be improved even if the co-located block in the
20- backward reference picture has only the backward motion vector.
Accordingly, coding efficiency can be improved. In addition, by
using a picture referred to by the backward motion vector as a
forward reference picture, and a reference picture which is
temporally closest available in display order as a backward
reference picture, coding efficiency can be increased.
Next, the fifth example of the direct mode will be explained
with reference to Fig. 8A. Fig. 8A is an illustration showing motion
vectors in direct mode, and specifically showing the case where the
block a of the picture B6 is coded in direct mode. In this case, on
the assumption that the value of the motion vectors is "0",
bi-predictive reference is performed for motion compensation, using
the picture P5 as a forward reference picture and the picture B7 as
28
CA 02762075 2011-12-16
a backward reference picture.
As mentioned above, by forcing the motion vector "0" in direct
mode, when the direct mode is selected, there is no need to transmit
the motion vector information nor to scale the motion vector, and
thus the processing volume can be reduced.
Next, the sixth example of the direct mode will be explained
with reference to Fig. 8B. Fig. 8B is an illustration showing motion
vectors in direct mode, and specifically showing the case where the
block a in the picture B6 is coded in direct mode. In this case, the
io motion vector g which has been used for coding the block f in the
picture P9 is utilized. The picture P9 is located later than the
picture B6, and the block f is co-located with the block a in the
picture B6. The motion vector g is stored in the motion vector
storage unit 116. The block a is bi-predicted from the forward
reference picture P5 and the backward reference picture B7 using
motion vectors generated utilizing the motion vector g. For
example, if a method of generating motion vectors parallel to the
motion vector g is used, as is the case of the above-mentioned first
example, motion vectors used for coding the block a are the motion
vector h and the motion vector i for the picture P5 and the picture B7
respectively for coding the block a.
In this case, where the forward motion vector h is MVF, the
backward motion vector i is MVB, the motion vector g is MV, the
temporal distance between the picture P9 which is located later in
display order than the current picture B6 and the picture P5 which
the block f in the picture P9 refers to is TRD, the temporal distance
between the current picture B6 and the forward reference picture P5
is TRF, and the temporal distance between the current picture B6
and the backward reference picture B7 is TRB respectively, the
motion vector h MVF and the motion vector i MVB are respectively
calculated by Equation 1 and Equation S.
MVB = - TRB x MV / TRD ...... Equation 5
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CA 02762075 2011-12-16
As described above, in direct mode, by scaling the motion
vector of the P-picture which is located later in display order, there
is no need to store the motion vector of a B-picture if the B-picture
is the backward reference picture, and there is also no need to
transmit the motion vector information. In addition, by using
reference pictures which are temporally closest in display order as a
forward reference picture and a backward reference picture, coding
efficiency can be increased.
Next, the seventh example of the direct mode will be
1o explained with reference to Fig. 8C. Fig. 8C is an illustration
showing motion vectors in direct mode, and specifically showing the
case where the block a in the picture B6 is coded in direct mode.
This example shows the case where the above-mentioned
assignment of relative indices to the picture numbers is changed
(remapped) and the picture P9 is a backward reference picture. In
this case, the motion vector g which has been used for coding the
block fin the picture P9 is utilized. The picture P9 is the backward
reference picture for the picture B7, and the block f is co-located
with the block a in the picture B6. The motion vector g is stored in
the motion vector storage unit 116. The block a is bi-predicted
from the forward reference picture P5 and the backward reference
picture P9 using motion vectors generated utilizing the motion
vector g. For example, if a method of generating motion vectors
parallel to the motion vector g, as is the case of the
above-mentioned first example, motion vectors used for coding the
block a are the motion vector h and the motion vector i for the
picture P5 and the picture P9 respectively.
In this case, where the forward motion vector h is MVF, the
backward motion vector i is MVB, the motion vector g is MV, the
temporal distance between the backward reference picture P9 for
the current picture B6 and the picture P5 which the block f in the
picture P9 refers to is TRD, and the temporal distance between the
CA 02762075 2011-12-16
current picture B6 and the forward reference picture P5 is TRF
respectively, the motion vector h MVF and the motion vector i MVB
are respectively calculated by Equation 1 and Equation 2.
As described above, in direct mode, the motion vector of the
previously coded picture can be scaled even if the relative indices to
the picture numbers are remapped, and when the direct mode is
selected, there is no need to transmit the motion vector information.
When the block a in the picture B6 is coded in direct mode, the
block in the backward reference picture for the picture B6 which is
co-located with the block a is coded by the forward reference only,
bi-predictive reference, or direct mode. And when a forward
motion vector has been used for this coding, this forward motion
vector is scaled, and the block a is coded in direct mode, as is the
case of the above-mentioned first, second or seventh example. On
the other hand, when the block co-located with the block a has been
coded by backward reference only using a backward motion vector,
this backward motion vector is scaled, and the block a is coded in
direct mode, as is the case of the above-mentioned third or fourth
example.
Above-mentioned direct mode is applicable not only to the
case where a time interval between pictures is fixed but also to the
case where it is variable.
The mode selection unit 109 outputs the determined coding
mode to the bit stream generation unit 104. Also, the mode
selection unit 109 generates predictive image data based on the
determined coding mode and outputs it to the difference calculation
unit 102. However, if selecting intra picture coding, the mode
selection unit 109 does not output predictive image data. The
mode selection unit 109 controls the switches 111 and 112 so as to
3o be connected to "a" side and "c" side respectively if selecting intra
picture coding, and controls the switches 111 and 112 so as to be
connected to "b" side and "d" side if selecting inter picture prediction
31
CA 02762075 2011-12-16
coding or a direct mode. If the determined coding mode is inter
picture prediction coding, the mode selection unit 109 outputs the
motion vectors used for the inter picture prediction coding to the bit
stream generation unit 104. Since the picture B6 is not used as a
reference picture for coding other pictures, there is no need to store
the motion vectors used for the inter picture prediction coding in the
motion vector storage unit 116. The case will be explained below
where the mode selection unit 109 selects the inter picture
prediction coding or the direct mode.
The difference calculation unit 102 receives the image data of
the macroblock in the picture B6 read out from the reordering
memory 101 and the predictive image data outputted from the mode
selection unit 109. The difference calculation unit 102 calculates
the difference between the image data of the macroblock in the
picture B6 and the predictive image data and generates the residual
error image data for outputting to the residual error coding unit 103.
The residual error coding unit 103 performs coding processing such
as frequency transform and quantization on the inputted residual
error image data, and thus generates the coded data for outputting
to the bit stream generation unit 104.
The bit stream generation unit 104 performs variable length
coding or the like on the inputted coded data, further adds
information such as motion vectors and a coding mode and so on to
the data, and generates the bit stream for outputting.
That is the completion of coding one macroblock in the picture
B6. According to the same processing, the remaining macroblocks
in the picture B6 are coded. And after all the macroblocks in the
picture B6 are coded, the picture B8 is coded.
(Coding of Picture B8)
Since a picture B8 is a B-picture, inter picture prediction
coding is performed for the picture B8 with reference to two
previously processed pictures located earlier or later than B6 in
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CA 02762075 2011-12-16
display order. The B-picture B8 refers to the picture B7 as a
forward reference picture and the picture P9 as a backward
reference picture, as described above. Since the picture B8 is not
used as a reference picture for coding other pictures, the coding
control unit 110 controls the switch 113 to be ON and the switches
114 and 115 to be OFF, which causes the macroblocks in the picture
B8 read out from the reordering memory 101 to be inputted to the
motion vector estimation unit 108, the mode selection unit 109 and
the difference calculation unit 102.
io Using the decoded picture data of the picture B7 and the
decoded picture data of the picture P9 which are stored in the
reference picture memory 107 as a forward reference picture and a
backward reference picture respectively, the motion vector
estimation unit 108 estimates the forward motion vector and the
backward motion vector for the macroblock in the picture B8. And
the motion vector estimation unit 108 outputs the estimated motion
vectors to the mode selection unit 109.
The mode selection unit 109 determines the coding mode for
the macroblock in the picture B8 using the motion vectors estimated
by the motion vector estimation unit 108.
Here, the case where the macroblock in the picture B8 is
coded using the direct mode will be explained with reference to Fig.
8D. Fig. 8D is an illustration showing motion vectors in direct mode,
and specifically showing the case where a block a in the picture B8
is coded in direct mode. In this case, a motion vector c which has
been used for coding a block b in the backward picture P9 is utilized.
The reference picture P9 is located later than the picture B8, and the
block b in the picture P9 is co-located with the block a. Here, it is
assumed that the block b has been coded by forward reference and-
the forward motion vector for the block b is the motion vector c.
The motion vector c is stored in the motion vector storage unit 116.
The block a is bi-predicted from the forward reference picture B7
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CA 02762075 2011-12-16
and the backward reference picture P9 using motion vectors
generated utilizing the motion vector c. For example, if a method
of generating motion vectors parallel to the motion vector c is used,
as is the case of the above-mentioned picture B7, the motion vector
d and the motion vector e are used for the picture B7 and the picture
P9 respectively for coding the block a.
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
temporal distance between the backward reference picture P9 for
1o the current picture B8 and the picture P5 which the block b in the
backward reference picture P9 refers to is TRD, the temporal
distance between the current picture B8 and the forward reference
picture B7 is TRF, and the temporal distance between the current
picture B8 and the backward reference picture P9 is TRB respectively,
the motion vector d MVF and the motion vector e MVB are
respectively calculated by Equation 1 and Equation 5.
As described above, in direct mode, by scaling the forward
motion vector of the backward reference picture, when the direct
mode is selected, there is no need to transmit the motion vector
information and the motion prediction efficiency can be improved.
Accordingly, coding efficiency can be improved. In addition, by
using reference pictures which are temporally closest available in
display order as forward and backward reference pictures, coding
efficiency can be increased.
Above-mentioned direct mode is applicable not only to the
case where a time interval between pictures is fixed but also to the
case where it is variable.
The mode selection unit 109 outputs the determined coding
mode to the bit stream generation unit 104. Also, the mode
3o selection unit 109 generates predictive image data based on the
determined coding mode and outputs it to the difference calculation
unit 102. However, if selecting intra picture coding, the mode
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CA 02762075 2011-12-16
selection unit 109 does not output predictive image data. The
mode selection unit 109 controls the switches 111 and 112 so as to
be connected to "a" side and "c" side respectively if selecting intra
picture coding, and controls the switches 111 and 112 so as to be
connected to "b" side and "d" side if selecting inter picture prediction
coding or direct mode. If the determined coding mode is inter
picture prediction coding, the mode selection unit 109 outputs the
motion vectors used for the inter picture prediction coding to the bit
stream generation unit 104. Since the picture B8 is not be used as
io a reference picture for coding other pictures, there is no need to
store the motion vectors used for the inter picture prediction coding
in the motion vector storage unit 116. The case will be explained
below where the mode selection unit 109 selects the inter picture
prediction coding or direct mode.
The difference calculation unit 102 receives the image data of
the macroblock in the picture B8 read out from the reordering
memory 101 and the predictive image data outputted from the mode
selection unit 109. The difference calculation unit 102 calculates
the difference between the image data of the macroblock in the
picture B8 and the predictive image data and generates the residual
error image data for outputting to the residual error coding unit 103.
The residual error coding unit 103 performs coding processing such
as frequency transform and quantization on the inputted residual
error image data and thus generates the coded data for outputting
to the bit stream generation unit 104.
The bit stream generation unit 104 performs variable length
coding or the like on the inputted coded data, further adds
information such as motion vectors and a coding mode and so on to
the data, and generates the bit stream for outputting.
That is the completion of coding one macroblock in the picture
B8. According to the same processing, the remaining macroblocks
in the picture B8 are coded.
CA 02762075 2011-12-16
According to the above-mentioned respective coding
procedures for the pictures P9, B7, B6 and B8, other pictures are
coded depending on their picture types and temporal locations in
display order.
In the above-mentioned embodiment, the moving picture
coding method according to the present invention has been
explained taking the case where the picture prediction structure as
shown in Fig. 6A is used as an example. Fig. 12 is an illustration
showing this picture prediction structure hierarchically. In Fig. 12,
1o arrows indicate prediction relations, in which the pictures pointed by
the arrows refer to the pictures located at the origins of the arrows.
In the picture prediction structure as shown in Fig. 6A, the coding
order is determined by giving a top priority to the pictures which are
farthest from the previously processed pictures in display order, as
shown in Fig. 12. For example, the picture farthest from an
I-picture or a P-picture is that located in the center of the
consecutive B-pictures. Therefore, if the picture P5 and P9 have
been coded, the picture B7 is to be coded next. And if the pictures
P5, B7 and P9 have been coded, the pictures B6 and B8 are to be
coded next.
In addition, the moving picture coding method according to
the present invention can be used for other picture prediction
structures than those as shown in Fig. 6 and Fig. 12, so as to
produce the effects of the present invention. Figs. 9-11 show the
examples of other picture prediction structures.
Fig. 9 shows the case where 3 B.-pictures are located between
I-pictures and P-pictures and the B-picture closest from the
previously processed picture is selected for coding first. Fig. 9A is
a diagram showing prediction relations between respective pictures
3o arranged in display order, and Fig. 9B is a diagram showing the
sequence of pictures reordered in coding order (a bit stream). Fig.
13 is a hierarchical diagram of the picture prediction structure
36
CA 02762075 2011-12-16
corresponding to Fig. 9A. In the picture prediction structure as
shown in Fig. 9A, the pictures closest in display order from the
previously processed pictures are coded first, as shown in Fig. 13.
For example, if the pictures P5 and P9 have been coded, the pictures
B6 and B8 are to be coded next. If the pictures P5, B6, B8 and P9
have been coded, the picture B7 is to be coded next.
Fig. 10 shows the case where 5 B-pictures are located
between I-pictures and P-pictures and the B-picture which is
farthest from the previously processed picture is selected for coding
first. Fig. 10A is a diagram showing prediction relations between
respective pictures arranged in display order, and Fig. 1013 is a
diagram showing the sequence of pictures reordered in coding order
(a bit stream). Fig. 14 is a hierarchical diagram of the picture
prediction structure corresponding to Fig. 10A. In the picture
prediction structure as shown in Fig. 10A, the coding order is
determined by giving a top priority to the pictures farthest in display
order from the previously processed pictures, as shown in Fig. 14.
For example, the picture farthest from an I-picture or a P-picture is
the B-picture in the center of the consecutive B-pictures. Therefore,
if the pictures P7 and P13 have been coded, the picture B10 is to be
coded next. If the pictures P7, B10 and P13 have been coded, the
pictures B8, B9, 1311 and B12 are to be coded next.
Fig. 11 shows the case -where 5 B-pictures are located
between I-pictures and P-pictures and the B-picture which is closest
from the previously processed picture is selected for coding first.
Fig. 11A is a diagram showing prediction relations between
respective pictures arranged in display order, and Fig. 11B is a
diagram showing the sequence of pictures reordered in coding order
(a bit stream). Fig. 15 is a hierarchical diagram of the picture
prediction structure corresponding to Fig. 11A. In the picture
prediction structure as shown in Fig. 11A, the pictures closest in
display order from the previously processed pictures are coded first,
37
CA 02762075 2011-12-16
as shown in Fig. 15. For example, if the pictures P5 and P9 have
been coded, the pictures B8 and B12 are to be coded next. If the
pictures P5, B8, B12 and P9 have been coded, the pictures B9 and
B11 are to be coded next. Furthermore, if the pictures P5, B8, B9,
B11, B12 and P9 have been coded, the picture B10 is to be coded
next.
As described above, according to the moving picture coding
method of the present invention, when inter picture prediction
coding is performed on a plurality of B-pictures located between
to I-pictures and P-pictures using bi-predictive reference, they are
coded in another order than display order. For that purpose, the
pictures located as close to the current picture as possible in display
order are used as forward and backward pictures. As a reference
picture, a B-picture is also used if it is available. When a plurality of
B-pictures located between I-pictures and P-pictures are coded in
different order from display order, the picture farthest from the
previously processed picture is to be coded first. Or, when a
plurality of B-pictures located between I-pictures and P-pictures are
coded in different order from display order, the picture closest from
the previously processed picture is to be coded first.
According to the moving picture coding method of the present
invention, above-mentioned operation enables to use a picture
closer to a current B-picture in display order as a reference picture
for coding it. Prediction efficiency is thus increased -for motion
compensation and coding efficiency is increased.
In addition, according to the moving picture coding method of
the present invention, for coding a block in a B-picture in direct
mode with reference to a B-picture previously coded as a backward
reference picture, if the co-located block in the backward reference
3o B-picture has been coded by forward reference or bi-predictive
reference, a motion vector obtained by scaling the forward motion
vector of the backward reference B-picture is used as' a motion
38
CA 02762075 2011-12-16
vector in direct mode. .
As mentioned above, in direct mode, by scaling a forward
motion vector of a backward reference B-picture, there is no need to
transmit motion vector information, and prediction efficiency can be
increased. In addition, by using a reference picture temporally
closest in display order as a forward reference picture, coding
efficiency can be increased.
Or, if a co-located block in a backward reference B-picture is
coded in direct mode, a motion vector obtained by scaling the
1o forward motion vector substantially used in direct mode is used as a
motion vector in direct mode.
As mentioned above, in direct mode, by scaling a forward
motion vector of a backward reference B-picture which has been
substantially used for the direct mode coding, there is no need to
transmit motion vector information, and prediction efficiency can be
increased even if the co-located block in the backward reference
picture is coded in direct mode. In addition, coding efficiency can
be improved by using a temporally closest reference picture as a
forward reference picture.
Or, if a co-located block in a backward reference B-picture is
coded by backward reference, motion vectors obtained by scaling
the backward motion vector of the block is used as motion vectors in
direct mode.
As mentioned above, in direct mode, by scaling a backward
motion vector which has been used for coding a co-located block in
the backward reference B-picture, there is no need to transmit
motion vector information, and prediction efficiency can be
increased even if the co-located block in the backward reference
picture has only a backward motion vector. In addition, by using a
temporally closest reference picture as a forward reference picture,
coding efficiency can be improved.
Or, if a co-located block in a backward reference B-picture is
39
CA 02762075 2011-12-16
coded by backward reference, motion vectors obtained by scaling
the backward motion vector used for that coding, with reference to
the picture referred to by this backward motion vector and the
backward reference picture, are used as motion vectors in direct
mode.
As mentioned above, in direct mode, by scaling a backward
motion vector which has been used for coding a co-located block in
the backward reference B-picture, there is no need to transmit
motion vector information, and prediction efficiency can be
io increased even if the co-located block in the backward reference
picture has only a backward motion vector. Accordingly, coding
efficiency can be improved. In addition, by using a picture referred
to by the backward motion vector as a forward reference picture and
a reference picture temporally closest available in display order as a
backward reference picture, coding efficiency can be increased.
Or, in direct mode, a motion vector which is forced to be set to
"0" is used.
By forcing a motion vector to be set to "0" in direct mode,
when the direct mode is selected, there is no need to transmit the
motion vector information nor to scale the motion vector, and
therefore the processing volume can be reduced.
In addition, according to the moving picture coding method of
the present invention, for coding a block in a B-picture in direct
mode with reference to a B-picture which has been previously coded
as a backward reference picture, a motion vector obtained by scaling
the forward motion vector which has been used for coding the
co-located block in the later P-picture is used as a motion vector in
direct mode.
As mentioned above, in direct mode, by scaling a motion
vector of a later P-picture, if the backward reference picture is a
B-picture, there is no need to store the motion vectors of the
B-picture and there is no need to transmit the motion vector
CA 02762075 2011-12-16
information, and thus prediction efficiency can be increased. In
addition, by using a temporally closest reference picture as a
forward reference picture, coding efficiency can be improved.
When assignment of relative indices to picture numbers is
changed and a co-located block in a backward reference picture has
been coded by forward reference, motion vectors obtained by
scaling that forward motion vector are used as motion vectors in
direct mode.
As mentioned above, in direct mode, a motion vector of a
to previously coded picture can be scaled even if assignment of relative
indices to picture numbers is changed, and there is no need to
transmit motion vector information.
In the present embodiment, the case has been explained
where motion compensation is made in every 16 (horizontal) x 16
(vertical) pixels and residual error image data is coded in every 8
(horizontal) x 8 (vertical) pixels or 4 (horizontal) x 4 (vertical) pixels,
but other size (number of pixels included) may be applied.
Also, in the present embodiment, the case has been explained
where consecutive 3 or 5 B-pictures are located, but other number
of pictures may be located.
Further, in the present embodiment, the case has been
explained where one of intra picture coding, inter picture prediction
coding using motion vectors and inter picture prediction coding
without using motion vectors is selected as a coding mode for
P-pictures, and one of intra picture coding, inter picture prediction
coding using a forward motion vector, inter picture prediction coding
using a backward motion vector, inter picture prediction coding
using a bi-predictive motion vectors and direct mode is selected for
B-pictures, but other coding mode may be used.
Also, in the present embodiment, seven examples of direct
mode have been explained, but a method which is uniquely
determined in every macroblock or block may be used, or any of a
41
CA 02762075 2011-12-16
plurality of methods in every macroblock or block may be selected.
If a plurality of methods are used, information indicating which type
of direct mode has been used is described in a bit stream.
In addition, in the present embodiment, the case has been
explained where a P-picture is coded with reference to one
previously coded I or P-picture which is located temporally earlier or
later in display order than the current P-picture, and a B-picture is
coded with reference to two previously processed neighboring
pictures which are located earlier or later in display order than the
io current B-picture, respectively. However, in the case of a P-picture,
the P-picture may be coded with reference to at most one picture for
each block from among a plurality of previously coded I or P pictures
as candidate reference pictures, and in the case of a B-picture, the
B-picture may be coded with reference to at most two pictures for
each block from among a plurality of previously coded neighboring
pictures which are located temporally earlier or later in display order
as candidate reference pictures.
In addition, when storing motion vectors in the motion vector
storage unit 116, the mode selection unit 109 may store both
forward and backward motion vectors or only a forward motion
vector, if a current block is coded by bi-predictive reference or in
direct mode. If it stores only the forward motion vector, the volume
stored in the motion vector storage unit 116 can be reduced.
(Second Embodiment)
Fig. 16 is a block diagram showing a structure of a moving
picture decoding apparatus using a moving picture decoding method
according to an embodiment of the present invention.
As shown in Fig. 16, the moving picture decoding apparatus
includes a bit stream analysis unit 1401, a residual error decoding
unit 1402, a mode decoding unit 1403, a frame memory control unit
1404, a motion compensation decoding unit 1405, a motion vector
42
CA 02762075 2011-12-16
storage unit 1406, a frame memory 1407, an addition unit 1408 and
switches 1409 and 1410.
The bit stream analysis unit 1401 extracts various types of
data such as coding mode information and motion vector
information from the inputted bit stream. The residual error
decoding unit 1402 decodes the residual error coded data inputted
from the bit stream analysis unit 1401 and generates residual error
image data. The mode decoding unit 1403 controls the switches
1409 and 1410 with reference to the coding mode information
io extracted from the bit stream.
The frame memory control unit 1404 outputs the decoded
picture data stored in the frame memory 1407 as output pictures
based on the information indicating the display order of the pictures
inputted from the bit stream analysis unit 1401.
The motion compensation decoding unit 1405 decodes the
information of the reference picture numbers and the motion vectors,
and obtains motion compensation image data from the frame
memory 1407 based on the decoded reference picture numbers and
motion vectors. The motion vector storage unit 1406 stores motion
vectors.
The addition unit 1408 adds the residual error coded data
inputted from the residual error decoding unit 1402 and the motion
compensation image data inputted from the motion compensation
decoding unit 1405 for generating the decoded image data. The
frame memory 1407 stores the generated decoded image data.
Next, the operation of the moving picture decoding apparatus
as structured as above will be explained. Here, it is assumed that
the bit stream generated by the moving picture coding apparatus is
inputted to the--moving picture decoding apparatus. Specifically, it
is assumed that a P-picture refers to one previously processed
neighboring I or P-picture which is located earlier or later than the
current P-picture in display order, and a B-picture refers to two
43
CA 02762075 2011-12-16
previously coded neighboring pictures which are located earlier or
later than the current B-picture in display order.
In this case, the pictures in the bit stream are arranged in the
order as shown in Fig. 6B. Decoding processing of pictures P9, B7,
B6 and B8 will be explained below in this order.
(Decoding of Picture P9)
The bit stream of the picture P9 is inputted to the bit stream
analysis unit 1401. The bit stream analysis unit 1401 extracts
various types of data from the inputted bit stream. Here, various
io types of data mean mode selection information, motion vector
information and others. The extracted mode selection information
is outputted to the mode decoding unit 1403. The extracted motion
vector information is outputted to the motion compensation
decoding unit 1405. And the residual error coded data is outputted
to the residual error decoding unit 1402.
The mode decoding unit 1403 controls the switches 1409 and
1410 with reference to the coding mode selection information
extracted from the bit stream. If intra picture coding is selected as
a coding mode, the mode decoding unit 1403 controls the switches
1409 and 1410 so as to be connected to "a" side and "c" side
respectively. If inter picture prediction coding is selected as a
coding mode, the mode decoding unit 1403 controls the switches
1409 and 1410 so as to be connected to "b" side and "d" side
respectively.
The mode decoding unit 1403 also outputs the coding mode
selection information to the motion compensation decoding unit
1405. The case where the inter picture prediction coding is
selected as a coding mode will be explained below. The residual
error decoding unit 1402 decodes the inputted residual error coded
3o data to generate residual error image data. The residual error
decoding unit 1402 outputs the generated residual error image data
to the switch 1409. Since the switch 1409 is connected to "b" side,
44
CA 02762075 2011-12-16
the residual error image data is outputted to the addition unit 1408.
The motion compensation decoding unit 1405 obtains motion
compensation image data from the frame memory 1407 based on
the inputted motion vector information and the like. The picture P9
has been coded with reference to the picture P5, and the picture P5
has been already decoded and stored in the frame memory 1407.
So, the motion compensation decoding unit 1405 obtains the motion
compensation image data from the picture data of the picture P5
stored in the frame memory 1407, based on the motion vector
io information. The motion compensation image data generated in
this manner is outputted to the addition unit 1408.
When decoding P-pictures, the motion compensation
decoding unit 1405 stores the motion vector information in the
motion vector storage unit 1406.
The addition unit 1408 adds the inputted residual error image
data and motion compensation image data to generate decoded
image data. The generated decoded image data is outputted to the
frame memory 1407 via the switch 1410.
That is the completion of decoding one macroblock in the
picture P9. According to the same processing, the remaining
macroblocks in the picture P9 are decoded in sequence. And after
all the macroblocks in the picture P9 are decoded, the picture B7 is
decoded.
(Decoding of Picture B7)
Since the operations of the bit stream analysis unit 1401, the
mode decoding unit 1403 and the residual error decoding unit 1402
until generation of residual error image data are same as those for
decoding the picture P9, the explanation thereof will be omitted.
The motion compensation decoding unit 1405 generates
motion compensation image data based on the inputted motion
vector information and the like. The picture B7 is coded with
reference to the picture P5 as a forward reference picture and the
CA 02762075 2011-12-16
picture P9 as a backward reference picture, and these pictures P5
and P9 have already been decoded and stored in the frame memory
1407.
If inter picture bi-prediction coding is selected as a coding
mode, the motion compensation decoding unit 1405 obtains the
forward reference picture data from the frame memory 14õ07 based
on the forward motion vector information. It also obtains the
backward reference picture data from the frame memory 1407
based on the backward motion vector information. Then, the
io motion compensation decoding unit 1405 averages the forward and
backward reference picture data to generate motion compensation
image data.
When direct mode is selected as a coding mode, the motion
compensation decoding unit 1405 obtains the motion vector of the
picture P9 stored in the motion vector storage unit 1406. Using this
motion vector, the motion compensation decoding unit 1405 obtains
the forward and backward reference picture data from the frame
memory 1407. Then, the motion compensation decoding unit 1405
averages the forward and backward reference picture data to
generate motion compensation image data.
The case where the direct mode is selected as a coding mode
will be explained with reference to Fig. 7A again. Here, it is
assumed that the block a in the picture B7 is to be decoded and the
block b in the picture P9 is co-located with the block a. The motion
vector of the block b is the motion vector c, which refers to the
picture P5. In this case, the motion vector d which is obtained
utilizing the motion vector c and refers to the picture P5 is used as
a forward motion vector, and the motion vector e which is obtained
utilizing the motion vector c and refers to the picture P9 is used as
3o a backward motion vector. For example, as a method of utilizing
the motion vector c, there is a method of generating motion vectors
parallel to the motion vector c. The motion compensation image
46
CA 02762075 2011-12-16
data is obtained by averaging the forward and backward reference
data obtained based on these motion vectors.
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
temporal distance between the backward reference picture P9 for
the current picture B7 and the picture P5 which the block b in the
backward reference picture P9 refers to is TRD, and the temporal
distance between the current picture B7 and the forward reference
picture P5 is TRF respectively, the motion vector d MVF and the
io motion vector e MVB are respectively calculated by Equation 1 and
Equation 2, where MVF and MVB represent horizontal and vertical
components of the motion vectors respectively. Note that the
temporal distance between the pictures can be determined based on
the information indicating the display order (position) given to
respective pictures or the difference specified by the information.
The motion compensation image data generated in this
manner is outputted to the addition unit 1408. The motion
compensation decoding unit 1405 stores the motion. vector
information in the motion vector storage unit 1406.
The addition unit 1408 adds the inputted residual error image
data and the motion compensation image data to generate decoded
image data. The generated decoded image data is outputted to the
frame memory 1407 via the switch 1410.
That is the completion of decoding one macroblock in the
picture B7. According to the same processing, the remaining
macroblocks in the picture B7 are decoded in sequence. And after
all the macroblocks of the picture B7 are decoded, the picture B6 is
decoded.
(Decoding of Picture B6)
Since the operations of the bit stream analysis unit 1401, the
mode decoding unit 1403 and the residual error decoding unit 1402
until generation of residual error image data are same as those for
47
CA 02762075 2011-12-16
decoding the picture P9, the explanation thereof will be omitted.
The motion compensation decoding unit 1405 generates
motion compensation image data based on the inputted motion
vector information and the like. The picture B6 has been coded
with reference to the picture P5 as a forward reference picture and
the picture B7 as a backward reference picture, and these. pictures
P5 and B7 have been already decoded and stored in the frame
memory 1407.
If inter picture bi-prediction coding is selected as a coding
io mode, the motion compensation decoding unit 1405 obtains the
forward reference picture data from the frame memory 1407 based
on the forward motion vector information. It also obtains the
backward reference picture data from the frame memory 1407
based on the backward motion vector information. Then, the
motion compensation decoding unit 1405 averages the forward and
backward reference picture data to generate motion compensation
image data.
When the direct mode is selected as a coding mode, the
motion compensation decoding unit 1405 obtains the motion vector
of the picture B7 stored in the motion vector storage unit 1406.
Using this motion vector, the motion compensation decoding unit
1405 obtains the forward and backward reference picture data from
the frame memory 1407. Then, the motion compensation decoding
unit 1405 averages the forward and backward reference picture data
to generate motion compensation image data.
The first example of the case where the direct mode is
selected as a coding mode will be explained with reference to Fig. 7B
again. Here, it is assumed that the block a in the picture B6 is to be
decoded and the block b in the picture B7 is co-located with the
3o block a. The block b has been coded by forward reference inter
picture prediction or bi-predictive reference inter picture prediction,
and the forward motion vector of the block b is the motion vector c,
48
CA 02762075 2011-12-16
which refers to the picture P5. In this case, the motion vector d
which is obtained utilizing the motion vector c and refers to the
picture P5 is used as a forward motion vector, and the motion vector
e which is obtained utilizing the motion vector c and refers to the
picture B7 is used as a backward motion vector. For example, as a
method of utilizing the motion vector c, there is a method of
generating motion vectors parallel to the motion vector c. The
motion compensation image data- is obtained by averaging the
forward and backward reference picture data obtained based on
1o these motion vectors d and e.
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
temporal distance between the backward reference picture B7 for
the current. picture B6 and the picture P5 which the block b in the
backward reference picture B7 refers to is TRD, and the temporal
distance between the current picture B6 and the forward reference
picture P5 is TRF respectively, the motion vector d MVF and the
motion vector e MVB are respectively calculated by Equation 1 and
Equation 2. Note that the temporal distance between pictures may
be determined based on the information indicating the display order
(position) of the pictures or the difference specified by the
information. Or, as the values of TRD and TRF, predetermined
values for respective pictures may be used. These predetermined
values may be described in the bit stream as header information.
The second example of the case where the direct mode is
selected as a coding mode will be explained with reference to Fig. 7B
again.
In this example, the motion vector which has been used for
decoding the block b in the picture B7 is utilized. The picture B7 is
the backward reference picture for the current picture B6, and the
block b is co-located with the block a in the picture B6. Here, it is
assumed that the block b has been coded in direct mode and the
49
CA 02762075 2011-12-16
motion vector c has been substantially used as a forward motion
vector for that coding. The motion vector c stored in the motion
vector storage unit 1406 may be used, or it is calculated by reading
out from the motion vector storage unit 1406 the motion vector of
the picture P9 which has been used for coding the block b in direct
mode, and then scaling that motion vector. Note that when storing
motion vectors in the motion vector storage unit 1406, the motion
compensation decoding unit 1405 needs to store only the forward
motion vector out of the two motion vectors obtained by scaling for
1o decoding the block b in the picture B7 in direct mode.
In this case, for the block a, the motion vector d which is
generated utilizing the motion vector c and refers to the picture P5
is used as a forward motion vector, and the motion vector e which is
generated utilizing the motion vector c and refers to the picture B7
is used as a backward motion vector. For example, as a method of
utilizing the motion vector c, there is a method of generating motion
vectors parallel to the motion vector c. The motion compensation
image data is obtained by averaging the forward and backward
reference picture data obtained based on these motion vectors d and
e.
In this case, the motion vector d MVF and the motion vector e
MVB are respectively calculated by Equation 1 and Equation 2, as is
the case of the first example of the direct mode.
Next, the third example of the case where the direct mode is
selected as a coding mode will be explained with reference to Fig. 7C
again.
In this example, it is assumed that the block a in the picture
B6 is to be decoded, and the block b in the picture B7 is co-located
with the block a. - The block b has been coded by backward
3o reference prediction, and the backward motion vector of the block b
is a motion vector f, which refers to the picture P9. In this case, for
the block a, the motion vector g which is obtained utilizing the
CA 02762075 2011-12-16
motion vector f and refers to the picture P5 is used as a forward
motion vector, and the motion vector h which is obtained utilizing
the motion vector f and refers to the picture B7 is used as a
backward motion vector. For example, as a method of utilizing the
motion vector f, there is a method of generating motion vectors
parallel to the motion vector f. The motion compensation image
data is obtained by averaging the forward and backward reference
picture data obtained based on these motion vectors g and h.
In this case where the forward motion vector g is MVF, the
to backward motion vector h is MVB, the motion vector f is MV, the
temporal distance between the backward reference picture B7 for
the current picture B6 and the picture P9 which the block b in the
backward reference picture B7 refers to is TRD, the temporal
distance between the current picture B6 and the forward reference
picture P5 is TRF, and the temporal distance between the current
picture B6 and the backward reference picture B7 is TRB respectively,
the motion vector g MVF and the motion vector h MVB are
respectively calculated by Equation 3 and Equation 4.
Next, the fourth example of the case where the direct mode is
selected as a coding mode will be explained with reference to Fig. 7D
again.
In this example, it is assumed that the block a in the picture
B6 is to be decoded, and the block b in the picture B7 is co-located
with the block a. The block b has been coded by backward
reference prediction as is the case of the third example, and the
backward motion vector of the block b is a motion vector f, which
refers to the picture P9. In this case, the motion vector g which is
obtained utilizing the motion vector f and refers to the picture P9 is
used as a forward motion vector, and the motion vector h which is
obtained utilizing the motion vector f and refers to the picture B7 is
used as a backward motion vector. For example, as a method of
utilizing the motion vector f, there is a method of generating motion
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CA 02762075 2011-12-16
vectors parallel to the motion vector f. The motion compensation
image data is obtained by averaging the forward and backward
reference picture data obtained based on these motion vectors g and
h.
In this case where the forward motion vector g is MVF, the
backward motion vector h is MVB, the motion vector f is MV, the
temporal distance between the backward reference picture B7 for
the current picture B6 and the picture P9 which the block b in the
backward reference picture B7 refers to is TRD, and the temporal
lo distance between the current picture B6 and the reference picture
P9 which the block b in the backward reference picture B7 refers to
is TRF respectively, the motion vector g MVF and the motion vector
h MVB are respectively calculated by Equation 1 and Equation 2.
Furthermore, the fifth example of the case where the direct
mode is selected as a coding mode will be explained with reference
to Fig. 8A again. Here, it is assumed that a block a in the picture B6
is to be decoded in direct mode. In this example, the motion vector
is set to zero "0", and motion compensation is performed by
bi-predictive reference using the picture P5 as a forward reference
picture and the picture B7 as a backward reference picture.
Next, the sixth example of the case where the direct mode is
selected as a coding mode will be explained with reference to Fig. 8B
again. Here, it is assumed that a block a in the picture B6 is to be
decoded in direct mode. In this example, the motion vector g which
has been used for decoding the block fin the P-picture P9 is utilized.
The picture P9 is located later than the current picture B6, and the
block f is co-located with the block a. The motion vector g is stored
in the motion vector storage unit 1406. The block a is bi-predicted
from the forward reference picture P5 and the backward reference
picture B7 using the motion vectors which are obtained utilizing the
motion vector g. For example, if a method of generating motion
vectors parallel to the motion vector g is used, as is the case of the
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above-mentioned first example, the motion vector h and the motion
vector i are used for the picture P5 and the picture B7 respectively
for obtaining the motion compensation image data of the block a.
In this case where the forward motion vector h is MVF, the
backward motion vector i is MVB, the motion vector g is MV, the
temporal distance between the picture P9 located later than the
current picture B6 and the picture P5 which the block fin the picture
P9 refers to is TRD, the temporal distance between the current
picture B6 and the forward reference picture P5 is TRF, and the
to temporal distance between the current picture B6 and the backward
reference picture B7 is TRB respectively, the motion vector h MVF
and the motion vector i MVB are respectively calculated by Equation
1 and Equation 5.
Next, the seventh example of the case where the direct mode
is selected as a coding mode will be explained with reference to Fig.
8C again. Here, it is assumed that a block a in the picture B6 is
decoded in direct mode. In this example, the assignment of
relative indices to the above-mentioned picture numbers is changed
(remapped) and the picture P9 is the backward reference picture.
In this case, the motion vector g which has been used for coding the
block fin the picture P9 is utilized. The picture P9 is the backward
reference picture for the picture B6, and the block f is co-located
with the block a in the picture B6. The motion vector g is stored in
the motion vector storage unit 1406. The block a is bi-predicted
from the forward reference picture P5 and the backward reference
picture P9 using motion vectors generated utilizing the motion
vector g. For example, if a method of generating motion vectors
parallel to the motion vector g is used, as is the case of the
above-mentioned first example, the motion vector h and the motion
vector i are used for the picture P5 and the picture P9 respectively
for obtaining the motion compensation image data of the block a.
In this case, where the forward motion vector h is MVF, the
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CA 02762075 2011-12-16
backward motion vector i is MVB, the motion vector g is MV, the
temporal distance between the backward reference picture P9 for
the current picture B6 and the picture P5 which the block f in the
picture P9 refers to is TRD, and the temporal distance between the
current picture B6 and the forward reference picture P5 is TRF
respectively, the motion vector h MVF and the motion vector i MVB
are respectively calculated by Equation 1 and Equation 2.
The motion compensation image data generated as above is
outputted to the addition unit 1408. The addition unit 1408 adds
io the inputted residual error image data and the motion compensation
image data to generate decoded image data. The generated
decoded image data is outputted to the frame memory 1407 via the
switch 1410.
That is the completion of decoding one macroblock in the
picture B6. According to the same processing, the remaining
macroblocks in the picture B6 are decoded in sequence. And after
all the macroblocks in the picture B6 are decoded, the picture B8 is
decoded.
(Decoding of Picture B8)
Since the operations of the bit stream analysis unit 1401, the
mode decoding unit 1403 and the residual error decoding unit 1402
until generation of residual error image data are same as those for
decoding the picture P9, the explanation thereof will be omitted.
The motion compensation decoding unit 1405 generates
motion compensation image data based on the inputted motion
vector information and the like. The picture B8 has been coded
with reference to the picture B7 as a forward reference picture and
the picture P9 as a backward reference picture, and these pictures
B7 and P9 have been already decoded and stored in the frame
memory 1407.
If inter picture bi-prediction coding is selected as a coding
mode, the motion compensation decoding unit 1405 obtains the
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forward reference image data from the frame memory 1407 based
on the forward motion vector information. It also obtains the
backward reference image data from the frame memory 1407 based
on the backward motion vector. information. Then, the motion
compensation decoding unit 1405 averages the forward and
backward reference image data to generate motion compensation
image data.
When direct mode is selected as a coding mode, the motion
compensation decoding unit 1405 obtains the motion vector of the
io picture P9 stored in the motion vector storage unit 1406. Using this
motion vector, the motion compensation decoding unit 1405 obtains
the forward and backward reference image data from the frame
memory 1407. Then, the motion compensation decoding unit 1405
averages the forward and backward reference picture data to
generate motion- compensation image data.
The case where the direct mode is selected as a coding mode
will be explained with reference to Fig. 8D again. Here, it is
assumed that a block a in the picture B8 is to be decoded and a block
b in the backward reference picture P9 is co-located with the block a.
The forward motion vector of the block b is the motion vector c,
which refers to the picture P5. In this case, the motion vector d
which is generated utilizing the motion vector c and refers to the
picture B7 is used as a forward motion vector, and the motion vector
e which is generated utilizing the motion vector c and refers to the
picture P9 is used as a backward motion vector. For example, as a
method of utilizing the motion vector c, there is a method of
generating motion vectors parallel to the motion vector c. The
motion compensation image data is obtained by averaging the
forward and backward reference image data obtained based on
these motion vectors d and e.
In this case where the forward motion vector d is MVF, the
backward motion vector e is MVB, the motion vector c is MV, the
CA 02762075 2011-12-16
temporal distance between the backward reference picture P9 for
the current picture B8 and the picture P5 which the block b in the
backward reference picture P9 refers to is TRD, the temporal
distance between the current picture B8 and the forward reference
picture B7 is TRF, and the temporal distance between the current
picture B8 and the backward reference picture P9 is TRB respectively,
the motion vector d MVF and the motion vector e MVB are
respectively calculated by Equation 1 and Equation 5.
The motion compensation image data generated in this
to manner is outputted to the addition unit 1408. The addition unit
1408 adds the inputted residual error image data and the motion
compensation image data to generate decoded image data. The
generated decoded image data is outputted to the frame memory
1407 via the switch 1410.
That is the completion of decoding one macroblock in the
picture B8. According to the same processing, the remaining
macroblocks in the picture B8 are decoded.in sequence. The other
pictures are decoded depending on their picture types according to
the above-mentioned decoding procedures.
Next, the frame memory control unit 1404 reorders the
picture data of the pictures stored in the frame memory 1407 in time
order as shown in Fig. 6A for outputting as output pictures.
As described above, according to the moving picture decoding
method of the present invention, a B-picture which has been coded
by inter picture bi-prediction is decoded using previously decoded
pictures which are located close in display order as forward and
backward reference pictures.
When the direct mode is selected as a coding mode, reference
image data is obtained from previously decoded image data to
obtain motion compensation image data, with reference to a motion
vector of a previously decoded backward reference picture stored in
the motion vector storage unit 1406.
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According to this operation, when a B-picture has been coded
by inter picture bi-prediction using pictures which are located close
in display order as forward and backward reference pictures, the bit
stream generated as a result of such coding can be properly
decoded.
In the present embodiment, seven examples of the direct
mode have been explained. However, one method, which is
uniquely determined for every macroblock or block based on the
decoding method of a co-located block in a backward reference
io picture, may be used, or a plurality of different methods may be
used for every macroblock or block by switching them. When a
plurality of methods are used, the macroblock or the block is
decoded using information described in a bit stream, indicating
which type of, direct mode has been used. For that purpose, the
operation of the motion compensation decoding unit 1405 depends.
upon the information. For example, when this information is added
for every block of motion compensation, the mode decoding unit
1403 determines which type of direct mode is used for coding and
delivers it to the motion compensation decoding unit 1405. The
motion compensation decoding unit 1405 performs decoding
processing using the decoding method as explained in the present
embodiment depending upon the delivered type of direct mode.
Also, in the present embodiment, the picture structure where
three B-pictures are located between I-pictures and P-pictures has
been explained, but any other number, four or five, for instance, of
B-pictures may be located.
In addition, in the present embodiment, the explanation has
been made on the assumption that a P-picture is coded with
reference to one previously coded I or P-picture which is located
3o earlier or later than the current P-picture in display order, a
B-picture is coded with reference to two previously coded
neighboring pictures which are located earlier or later than the
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CA 02762075 2011-12-16
current B-picture in display order, and the bit stream generated as a
result of this coding is decoded. However, in the case of a P-picture,
the P-picture may be coded with reference to at most one picture for
each block from among a plurality of previously coded I or P pictures
which are located temporally earlier or later in display order as
candidate reference pictures, and in the case of a B-picture, the
B-picture may be coded with reference to at most two pictures for
each block from among a plurality of previously coded neighboring
pictures which are located temporally earlier or later in display order
io as candidate reference pictures.
Furthermore, when storing motion vectors in the motion
vector storage unit 1406, the motion compensation decoding unit
1405 may store both forward and backward motion vectors, or store
only the forward motion vector, if a current block is coded by
bi-predictive reference or in direct mode. If only the forward
motion vector is stored, the memory volume of the motion vector
storage unit 1406 can be reduced.
(Third Embodiment)
If a program for realizing the structures of the moving picture
coding method or the moving picture decoding method as shown in
the above embodiments is recorded on a memory medium such as a
flexible disk, it becomes possible to perform the processing as
shown in these embodiments easily in an independent computer
system.
Fig. 17 is an illustration showing the case where the
processing is performed in a' computer system using a flexible disk
which stores the moving picture coding method or the moving
picture decoding method of the above embodiments.
30- Fig. 17B shows a front view and a cross-sectional view of an
appearance of a flexible disk, and the flexible disk itself, and Fig.
17A shows an example of a physical format of a flexible disk as a
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recording medium body. The flexible disk FD is contained in a case
F, and a plurality of tracks Tr are formed concentrically on the
surface of the disk in the radius direction from the periphery and
each track is divided * into 16 sectors Se in the angular direction.
Therefore, as for the flexible disk storing the above-mentioned
program, the moving picture coding method as the program is
recorded in an area allocated for it on the flexible disk FD.
Fig. 17C shows the structure for recording and reproducing
the program on and from the flexible disk FD. When the program is
recorded on the flexible disk FD, the moving picture coding method
or the moving picture decoding method as a program is written in
the flexible disk from the computer system Cs via a flexible disk
drive. When the moving picture coding method is constructed in
the computer system by the program on the flexible disk, the
program is read out from the flexible disk drive and transferred to
the computer system.
The above explanation is made on the assumption that a
recording medium is a flexible disk, but the same processing can
also be performed using an optical disk. In addition, the recording
medium is not limited to a flexible disk and an optical disk, but any
other medium such as an IC card and a ROM cassette capable of
recording a program can be used.
Following is the explanation of the applications of the moving
picture coding method and the moving picture decoding method as
shown in the above embodiments, and the system using them.
Fig. 18 is a block diagram showing the overall configuration of
a content supply system ex100 for realizing content distribution
service. The area for providing communication service is divided
into cells of desired size, and base stations ex107^-ex110 which are
fixed wireless stations are placed in respective cells.
In this content supply system ex100, devices such as a
computer ex111, a PDA (personal digital assistant) ex112, a camera
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ex113, a mobile phone ex114 and a camera-equipped mobile phone
ex115 are connected to the Internet ex 101 via an Internet service
provider ex102, a telephone network ex104 and base stations ex107
^-ex110.
However, the content supply system ex100 is not limited to
the configuration as shown in Fig. 18, and a combination of any of
them may be connected. Also, each device may be connected
directly to the telephone network ex104, not through the base
stations ex107^-ex110.
The camera ex113 is a device such as a digital video camera
capable of shooting moving pictures. The mobile phone may be a
mobile phone of a PDC (Personal Digital Communications) system, a
CDMA (Code Division Multiple Access) system, a W-CDMA
(Wideband-Code Division Multiple Access) system or a GSM (Global
System for Mobile Communications) system, a PHS (Personal
Handyphone system) or the like.
A streaming server ex103 is connected to the camera ex113
via the base station ex109 and the telephone network ex104, which
enables live distribution or the like using the camera ex113 based on
the coded data transmitted from a user. Either the camera ex113
or the server for transmitting the data may code the data. Also, the
moving picture data shot by a camera ex116 may be transmitted to
the streaming server ex103 via the computer ex111. The camera
ex116 is a device such as a digital camera capable of shooting still
and moving pictures. Either the camera ex116 or the computer
ex111 may code the moving picture data. An LSI ex117 included in
the computer ex111 or the camera ex116 actually performs coding
processing. Software for coding and decoding moving pictures may
be integrated into any type of storage medium (such as a CD-ROM,
3o a flexible disk and a hard disk) that is a recording medium which is
readable by the computer ex111 or the like. Furthermore, a
camera-equipped mobile phone ex115 may transmit the moving
CA 02762075 2011-12-16
picture data. This moving picture data is the data coded by the LSI
included in the mobile phone ex115.
The content supply system ex100 codes contents (such as a
music live video) shot by users using the camera ex113, the camera
ex116 or the like in the same manner as the above embodiment and
transmits them to the streaming server ex103, while the streaming
server ex103 makes stream distribution of the content data to the
clients at their request. The clients include the computer ex111,
the PDA ex112, the camera ex113, the mobile phone ex114 and so
lo. on capable of decoding the above-mentioned coded data. In the
content supply system exlOO, the clients can thus receive and
reproduce the coded data, and further can receive, decode and
reproduce the data in real time so as to realize personal
broadcasting.
When each device in this system performs coding or decoding,
the moving picture coding apparatus or the moving picture decoding
apparatus, as shown in the above-mentioned embodiment, can be
used.
A mobile phone will be explained as an example of the device.
Fig. 19 is a diagram showing the mobile phone ex115 using
the moving picture coding method and the moving picture decoding
method explained in the above embodiments. The mobile phone
ex115 has an antenna ex201 for sending and receiving radio waves
to and from the base station ex110, a camera unit ex203 such as a
CCD camera capable of shooting video and still pictures, a display
unit ex202 such as a liquid crystal display for displaying the data
obtained by decoding video and the like shot by the camera unit
ex203 and received by the antenna ex201, a body unit including a
set of operation keys ex204, a voice output unit ex208 such as a
speaker for outputting voices, a voice input unit 205 such as a
microphone for inputting voices, a storage medium ex207 for
storing coded or decoded data such as data of moving or still
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pictures shot by the camera, text data and data of moving or still
pictures of received e-mails, and a slot unit ex206 for attaching the
storage medium ex207 to the mobile phone ex115. The storage
medium ex207 includes a flash memory element, a kind of EEPROM
(Electrically Erasable and Programmable Read Only Memory) that is
an electrically erasable and rewritable nonvolatile memory, in a
plastic case such as a SD card.
The mobile phone ex115 will be further explained with
reference to Fig. 20. In the mobile phone ex115, a main control
1o unit ex311 for overall controlling the display unit ex202 and the
body unit including operation keys ex204 is connected to a power
supply circuit unit ex310, an operation input control unit ex304, a
picture coding unit ex312, a camera interface unit ex303, an LCD
(Liquid Crystal Display) control unit ex302, a picture decoding unit
ex309, a multiplex/demultiplex unit ex308, a record/reproduce unit
ex307, a modem circuit unit ex306 and a voice processing unit
ex305 to each other via a synchronous bus ex313.
When a call-end key or a power key is turned ON by a user's
operation, the power supply circuit unit ex310 supplies respective
units with power from a battery pack so as to activate the
camera-equipped digital mobile phone ex115 for making it into a
ready state.
In the mobile phone ex115, the voice processing unit ex305
converts the voice signals received by the voice input unit ex205 in
conversation mode into digital voice data under the control of the
main control unit ex311 including a CPU, ROM and RAM, the modem
circuit unit ex306 performs spread spectrum processing of the
digital voice data, and the send/receive circuit unit ex301 performs
digital-to-analog conversion and frequency transform of the data, so
3o as to transmit it via the antenna ex201. Also, in the mobile phone
ex115, after the data received by the antenna ex201 in conversation
mode is amplified and performed of frequency transform and
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CA 02762075 2011-12-16
analog-to-digital conversion, the modem circuit unit ex306
performs inverse spread spectrum processing of the data, and the
voice processing unit ex305 converts it into analog voice data, so as
to output it via the voice output unit 208.
Furthermore, when transmitting e-mail in data
communication mode, the text data of the e-mail inputted by
operating the operation keys ex204 on the body unit is sent out to
the main control unit ex311 via the operation input control unit
ex304. In the main control unit ex311, after the modem circuit unit
io ex306 performs spread spectrum processing of the text data and the
send/receive circuit unit ex301 performs digital-to-analog
conversion and frequency transform for it, the data is transmitted to
the base station ex110 via the antenna ex201.
When picture data is transmitted in data communication
mode, the picture data shot by the camera unit ex203 is supplied to
the picture coding unit ex312 via the camera interface unit ex303.
When it is not transmitted, it is also possible to display the picture
data shot by the camera unit ex203 directly on the display unit 202
via the camera interface unit ex303 and the LCD control unit ex302.
The picture coding unit ex312, which includes the moving
picture coding apparatus as explained in the present invention,
compresses and codes the picture data supplied from the camera
unit ex203 by the coding method used for the moving picture coding
apparatus as shown in the above embodiment so as to transform it
into coded picture data, and sends it out to the
multiplex/demultiplex unit ex308. At this time, the mobile phone
ex115 sends out the voices received by the voice input unit ex205
during shooting by the camera unit ex203 to the
multiplex/demultiplex unit ex308 as digital voice data via the voice
processing unit ex305.
The multiplex/demultiplex unit ex308 multiplexes the coded
picture data supplied from the picture coding unit ex312 and the
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CA 02762075 2011-12-16
voice data supplied from the voice processing unit ex305 by a
predetermined method, the modem circuit unit ex306 performs
spread spectrum processing of the multiplexed data obtained as a
result of the multiplexing, and the send/receive circuit unit ex301
performs digital-to-analog conversion and frequency transform of
the data for transmitting via the antenna ex201.
As for receiving data of a moving picture file which is linked to
a Web page or the like in data communication mode, the modem
circuit unit ex306 performs inverse spread spectrum processing of
1o the data received from the base station ex110 via the antenna
ex201, and sends out the multiplexed data obtained as a result of
the processing to the multiplex/demultiplex unit ex308.
In order to decode the multiplexed data received via the
antenna ex201, the multiplex/demultiplex unit ex308 separates the
multiplexed data into a bit stream of picture data and a bit stream of
voice data, and supplies the coded picture data to the picture
decoding unit ex309 and the voice data to the voice processing unit
ex305 respectively via the synchronous bus ex313.
Next, the picture decoding unit ex309, which includes the
moving picture decoding apparatus as explained in the present
invention, decodes the bit stream of picture data by the decoding
method corresponding to the coding method as shown in the
above-mentioned embodiment to generate reproduced moving
picture data, and supplies this data to the display unit ex202 via the
LCD control unit ex302, and thus moving picture data included in a
moving picture file linked to a Web page, for instance, is displayed.
At the same time, the voice processing unit ex305 converts the voice
data into analog voice data, and supplies this data to the voice
output unit ex208, and thus voice data included in a moving picture
file linked to a Web page, for instance, is reproduced.
The present invention is not limited to the above-mentioned
system, and at least either the moving picture coding apparatus or
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CA 02762075 2011-12-16
the moving picture decoding apparatus in the above-mentioned
embodiment can be incorporated into a digital broadcasting system
as shown in Fig. 21. Such ground-based or satellite digital
broadcasting has been in the news lately. More specifically, a bit
stream of video information is transmitted from a broadcast station
ex409 to or communicated with a broadcast satellite ex410 via radio
waves. Upon receipt of it, the broadcast satellite ex410 transmits
radio waves for broadcasting, a home-use antenna ex406 with a
satellite broadcast reception function receives the radio waves, and
to a television (receiver) ex401 or a set top box (STB) ex407 decodes
the bit stream for reproduction. The moving picture decoding
apparatus as shown in the above-mentioned embodiment can be
implemented in the reproduction device ex403 for reading off and
decoding the bit stream recorded on a storage medium ex402 that is
a recording medium such as a CD and DVD. In this case, the
reproduced video signals are displayed on a monitor ex404. It is
also conceived to implement the moving picture decoding apparatus
in the set top box ex407 connected to a cable ex405 for a cable
television or the antenna ex406 for satellite and/or ground-based
broadcasting so as to reproduce them on a monitor ex408 of the
television ex401. The moving picture decoding apparatus may be
incorporated into the television, not in the set top box. Or, a car
ex412 having an antenna ex411 can receive signals from the
satellite ex410 or the base station ex107 for reproducing moving
pictures on a display device such as a car navigation system ex413.
Furthermore, the moving picture coding apparatus as shown
in the above-mentioned embodiment can code picture signals for
recording on a recording medium. As a concrete example, there is
a recorder ex420 such as a DVD recorder for recording picture
signals on a DVD disc ex421 and a disk recorder for recording them
on a hard disk. They can be recorded on an SD card ex422. If the
recorder ex420 includes the moving picture decoding apparatus as
CA 02762075 2011-12-16
shown in the above-mentioned embodiment, the picture signals
recorded on the DVD disc ex421 or the SD card ex422 can be
reproduced for display on the monitor ex408.
As the structure of the car navigation system ex413, the
structure without the camera unit ex203, the camera interface unit
ex303 and the picture coding unit ex312, out of the units shown in
Fig. 20, is conceivable. The same goes for the computer ex111, the
television (receiver) ex401 and others.
In addition, three types of implementations can be conceived
io for a terminal such as the above-mentioned mobile phone ex114; a
sending/receiving terminal including both an encoder and a decoder,
a sending terminal including an encoder only, and a receiving
terminal including a decoder only.
As described above, it is possible to use the moving picture
coding method or the moving picture decoding method in the
above-mentioned embodiments in any of the above-mentioned
apparatus and system, and using this method, the effects described
in the above embodiments can be obtained.
Furthermore, the present invention is not limited to the above
embodiments, but may be varied or modified in many ways without
any departure from the scope of the present invention.
As described above, according to the moving picture coding
method of the present invention, B-pictures can be coded using
pictures which are temporally close in display order as reference
pictures. Accordingly, prediction efficiency for motion
compensation is improved and thus coding efficiency is improved.
In direct mode, by scaling a first motion vector of a second
reference picture, there is no need to transmit motion vector
information and thus prediction efficiency can be improved.
Similarly, in direct mode, by scaling a first motion vector
substantially used for the direct mode coding of the second
reference picture, there is no need to transmit motion vector
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CA 02762075 2011-12-16
information, and prediction efficiency can be improved even if a
co-located block in the second reference picture is coded in direct
mode.
Also, in direct mode, by scaling a second motion vector which
has been used for coding a co-located block in a second reference
picture, there is no need to transmit motion vector information, and
prediction efficiency can be improved even if the co-located block in
the second reference picture has only a second motion vector.
Furthermore, in direct mode, by setting forcedly a motion
io vector in direct mode to be "0", when the direct mode is selected,
there is no need to transmit motion vector information nor to scale
the motion vector, and thus processing volume can be reduced.
Also, in direct mode, by scaling a motion vector of a later
P-picture, there is no need to store a motion vector of a second
reference picture when the second reference picture is a B-picture.
And, there is no need to transmit the motion vector information, and
prediction efficiency can be improved.
Furthermore, in direct mode, since a first motion vector is
scaled if a second reference picture has the first motion vector, and
a second motion vector is scaled if the second reference picture does
not have the first motion vector but only the second motion vector,
there is no need to add motion vector information to a bit stream
and prediction efficiency can be improved.
In addition, according to the moving picture decoding method
of the present invention, a bit stream, which is generated as a result
of inter picture bi-prediction coding using pictures which are located
temporally close in display order as first and second reference
pictures, can be properly decoded.
Industrial Applicability
As described above, the moving picture coding method and
the moving picture decoding method according to the present
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invention are useful as a method for coding picture data
corresponding to pictures that form a moving picture to generate a
bit stream, and a method for decoding the generated bit stream,
using a mobile phone, a DVD apparatus and a personal computer, for
instance.
68
